1. Field of the Invention
The present invention relates to a mouse type input device which can detect the amount of movement due to an operating physical force, and more particularly to an input device which can reduce power consumption.
2. Description of the Related Art
Input devices for detecting the amount of movement thereof due to an operating physical force include the following types. Each of some type input devices has a ball-shaped or roller-shaped control element. The control element is rotated by a finger and the amount of rotation thereof is detected and is then transmitted to a host computer. Each of mouse type input devices includes a case. The case is moved while being held by a hand and the amount of movement thereof is detected.
These input devices have means for detecting the amount of movement. These detecting means have the similar structures. For example, according to the mouse type input device, a ball is rotatably held in the case. When the case is moved on a pad, the ball is rotated in association with the movement of the case. The case includes an X-axis encoder and a Y-axis encoder arranged perpendicularly to each other. The encoders are in contact with the ball and are rotated.
Each of the X-axis and Y-axis encoders has a rotary element. Each rotary element has light transmitting portions formed in the rotating direction at a predetermined pitch. A light source faces the side of each rotary element and a photodetector faces the other side of the rotary element. The photodetector intermittently receives light emitted from the light source in accordance with a rotating speed of the rotary element. The number of light receiving times of the photodetector within a predetermined time changes in accordance with the rotating speed of the rotary element. Thus, the amount of rotation of the rotary element within the predetermined time, namely, the rotating speed thereof can be detected.
Each of the X-axis encoder and the Y-axis encoder detects the amount of rotation within the predetermined time. Consequently, the amount of movement of the case and the moving speed thereof can be detected.
In the foregoing conventional input devices, generally, the light sources continuously emit light, resulting in large power consumption. It is uneconomical. Then, in some input devices, the light sources intermittently emit light every predetermined driving period, thus reducing power consumption.
On condition that the light sources intermittently emit light as mentioned above, when the case is moved at the highest speed and the rotary elements of the X-axis and Y-axis encoders are rotated at the highest speed, it is necessary to ensure resolution enough to detect the amount of movement of the case. Therefore, the driving period of each light source during which the rotating speed of the corresponding rotary element indicates the maximum value is determined as a reference. The driving period is fixed to the shortest value.
Accordingly, there are limits to which power necessary for light emission of each light source is reduced. For example, in the mouse type input device using a battery as a power supply or an input device mounted on a notebook-sized personal computer using a battery as a power supply, battery life is short.